A liquid crystal display panel includes a TFT substrate having pixel electrodes and thin film transistors (TFT) arranged in a matrix, and a counter substrate that is located opposite the TFT substrate, having color filters positioned corresponding to the pixel electrodes on the TFT substrate. A liquid crystal is interposed between the TFT substrate and the counter substrate to form a display region. An image is formed by controlling light transmittance through liquid crystal molecules for each pixel. Since the liquid crystal is capable of controlling only polarization light, a light ray from a backlight is polarized by a lower polarizer before incidence to the TFT substrate, and controlled by a liquid crystal layer. It is further polarized by an upper polarizer again so as to be emitted to the outside. Therefore the light emitted from the liquid crystal display panel becomes polarization light.
Various methods for forming a three-dimensional image on the liquid crystal display panel have been proposed. Among all of those methods, the one which provides the liquid crystal lens on the liquid crystal display panel has been focused on its application especially to a small-sized display device because of features that no special glasses are required for visual recognition of the three-dimensional image and that selection between the two-dimensional image and the three-dimensional image may be performed.
Japanese Patent No. 2862462 discloses the structure in which a liquid crystal lens has liquid crystal molecules interposed between an upper substrate and a lower substrate, upper substrate electrode patterns are formed in stripes on the upper substrate, and flat solid lower substrate electrode patterns are formed on the lower substrate so that the lens is formed through alignment of the liquid crystal molecules along the electric field generated by applying a voltage to both the upper and lower substrate electrode patterns.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-520231 discloses a liquid crystal lens that uses the electric field generated by a longitudinal electric field between the upper substrate electrode pattern and the lower substrate electrode pattern. Those upper and the lower substrate electrode patterns on the upper and lower substrates are similar, but an angle of 90° is formed therebetween through turning with each other. This makes it possible to make the lens to turn at 90° through the method of applying the voltage to the upper and lower substrate electrode patterns. The three-dimensional display may be performed both in horizontal and vertical modes.
FIGS. 10 to 13 schematically show a liquid crystal lens 10 and a 3D display using the liquid crystal lens 10. The terms “2D display” and “3D display” herein refer to the “two-dimensional display” and the “three-dimensional display”. The liquid crystal lens 10 has the same structure as the liquid crystal display element, which interposes the liquid crystal between two substrates which form electrodes. However, unlike the liquid crystal display for displaying purpose, it is not intended to be used for the control of polarization direction, and accordingly, no polarizer is used.
FIG. 10 schematically shows the electrodes formed on the two substrates that interpose the liquid crystal. The electrode on the lower substrate 30 has a transversely long rectangular pattern as indicated by a solid line, and the electrode on the upper substrate 20 has a rectangular pattern as indicated by a dashed line. Rectangular boxes A and B denote electrode terminals that externally apply the voltage. The line which connects the electrode terminal to the electrode on the aforementioned substrate denotes a wiring. The electrode connected to the electrode terminal A may be designated as an electrode A, and the electrode connected to the electrode terminal B may be designated as an electrode B. Basically, each pattern on the upper and lower substrates is not limited, and those patterns may be reversed with respect to the upper and lower substrates. Since transmission of light is required, the transparent electrode such as ITO is used for forming at least the electrode as shown by the dashed line, which entirely covers the display portion.
Arrow P1 shown in FIG. 10 denotes a rubbing direction on the lower substrate, and arrow P2 denotes a rubbing direction on the upper substrates. The interposed liquid crystal is aligned to have a part at a longer axis side directed toward the arrow direction when no voltage is applied. FIG. 11 is a sectional view taken along line Y-Y of FIG. 10. The electrodes on the lower substrate 30 are set so that two pixels of a liquid crystal display panel 100 below the liquid crystal lens 10 are arranged between two electrodes. Actually, a pitch of the two pixels is not the same as the pitch of the electrodes. Those pitches are appropriately designed in accordance with an assumed viewing position.
FIG. 11 illustrates a state where each voltage applied to the upper and lower electrodes is set to be the same, that is, no voltage is applied to the liquid crystal. In other words, the liquid crystal lens 10 is in an off-state. In this state, the liquid crystal is entirely in an alignment direction regulated through rubbing. The liquid crystal lens 10 as an optically uniform medium with respect to the transmitted light performs no action, while directly outputting the 2D image on the liquid crystal display panel 100.
FIG. 12 illustrates a state where the voltage is applied to the upper and lower electrodes of the liquid crystal lens 10 so as to change the alignment direction of the liquid crystal, that is, the liquid crystal lens 10 is in an on-state. Like the liquid crystal display panel 100 in a normal state, AC voltage is applied for preventing deterioration in the liquid crystal. The electrode on the upper substrate 20 is flat solid, and the lower electrodes locally exist. Therefore, the electric field applied to the liquid crystal is not uniform in the longitudinal and transverse directions. Along the radial (parabolic) electric field toward the upper solid electrode from the locally positioned lower electrodes, the liquid crystal molecules are also radially aligned as shown in the drawing.
A liquid crystal molecule 50 exhibits a birefringent property. Polarization light of transmitted light has the component in the longitudinal direction (longer axis direction) of the molecule brought into extraordinary light with high refractive index. The component orthogonal to the one in the longitudinal direction of the molecule is brought into ordinary light with lower refractive index than that of the extraordinary light. The intervening angle may be obtained through resolution into the extraordinary light component and the ordinary light component in the same manner as vector resolution. The birefringent property aligns the liquid crystal as shown in FIG. 12.
If a polarization direction 40 of the incident light, that is, the light emitted from the liquid crystal display panel 100 is substantially parallel to the rubbing direction on the liquid crystal lens 10, the ratio between the portion with high refractive index (extraordinary light) and the portion with low refractive index upon passage of the incident light through the liquid crystal lens 10 varies by location. As FIGS. 10 and 11 show, the longer axis direction of the liquid crystal molecule 50 is in line with the rubbing direction which determines an initial alignment of the liquid crystal.
Referring to FIG. 12, a dashed line representative of an interface of a convex lens 11 schematically shows the interface between the portion with high refractive index and the portion with low refractive index. The same effect as the one derived from the convex lens is obtained in the liquid crystal. When two pixels of the liquid crystal display panel 100 are provided under the effect of the convex lens as shown in FIG. 12, light rays from a first pixel 200 change the paths mainly to the right side, and light rays from a second pixel 300 change the paths mainly to the left side. Referring to FIG. 12, each of codes “r”, “g” and “b” of the first pixel 200 and the second pixel 300 denotes a “red sub-pixel”, a “green sub-pixel” and a “blue sub-pixel”, respectively, common to all the pixels. In the condition where the liquid crystal lens 10 and the liquid crystal display panel 100 are appropriately designed so that signals for a right eye and a left eye are displayed on the first pixel 200 and the second pixel 300, the light from the first pixel 200 and the light from the second pixel 300 may be guided to the right eye and the left eye of a viewer, respectively. This allows the viewer to recognize the 3D image.
FIG. 13 is a plan view representing a relationship between pixels of the liquid crystal display panel 100 for right and left eyes and low electrode patterns 31 of the liquid crystal lens. Referring to the liquid crystal display panel 100 in FIG. 13, the pixels for the right eye are designated as A1 to A4, and those for the left eye are designated as B1 to B4.
FIG. 14 illustrates the liquid crystal lens 10 with respect to the pattern configuration of the lower substrate electrode patterns 31 and the rubbing direction. Referring to FIG. 14, both the rubbing direction P1 on the upper substrate and the rubbing direction P2 on the lower direction are transverse. The polarization direction 40 of emission from the liquid crystal display panel is transverse as well. FIG. 15 is a sectional view of the liquid crystal lens 10 shown in FIG. 14 in a state where no voltage is applied between the upper substrate 20 and the lower substrate 30. FIG. 16 is a sectional view of the liquid crystal lens 10 in the state where the voltage is applied between the upper substrate 20 and the lower substrate 30.
A pair of polarized sunglasses as shown in FIG. 17 may be used when fishing on the seashore, for example, for preventing difficulty in viewing scenery owing to incidence of light reflected from the water surface. The transmission polarization axis of the polarized sunglasses is in a vertical direction as shown in FIG. 17. However, the emission polarization axis of the liquid crystal lens as shown in FIGS. 14 to 16 is transverse. When using the polarized sunglasses, the light ray that has passed through the liquid crystal lens may fail to pass through the polarized sunglasses. Accordingly, the viewer cannot see the image on the liquid crystal display device provided with the liquid crystal lens.
The polarization axis of the light ray that has passed through the liquid crystal lens as shown in FIGS. 14 to 16 is in an arrowed direction B shown in FIG. 18. Since the transmission polarization axis of the polarized sunglasses is vertical, the light that has passed through the liquid crystal lens shown in FIGS. 14 to 16 cannot be visually recognized through the polarized sunglasses. If the polarization axis of the light which has passed through the liquid crystal lens is in an arrowed direction A, the emitted light is allowed to pass through the polarized sunglasses.
FIGS. 19 to 21 show the liquid crystal lens having the polarization axis of the light emitted from the liquid crystal lens vertically directed. FIG. 19 illustrates the lower substrate electrode patterns 31 and the rubbing direction on the liquid crystal lens 10. Referring to FIG. 19, the rubbing direction P1 on the lower substrate and the rubbing direction P2 on the upper direction are vertical. The polarization axis of the light emitted from the liquid crystal display panel is also in the vertical direction. Accordingly, the light that has passed through the liquid crystal lens 10 as shown in FIGS. 19 to 21 may be visually recognized through the polarized sunglasses.
FIG. 20 shows the state where no voltage is applied between the upper substrate 20 and the lower substrate 30 of the liquid crystal lens 10 shown in FIG. 19. FIG. 21 shows the state where the voltage is applied between those substrates. Referring to FIG. 20, since the liquid crystal molecules are not modulated, the light emitted from the liquid crystal display panel 100 directly passes through the liquid crystal lens 10. Referring to FIG. 21, the voltage is applied between the upper substrate 20 and the lower substrate 30 to form the liquid crystal lens, which enables the 3D display. The polarization axis of the light passing through the liquid crystal lens 10 is in the vertical direction, which may be visually recognized through the polarized sunglasses.
Referring to FIG. 19, it is necessary to make a 90° turn of the liquid crystal molecules and align them along the electric field so as to form the convex lens using the liquid crystal molecules. The experimental results of the inventors have clarified the difficulty in forming the liquid crystal lens which enables the clear 3D display. This is mainly considered to be caused by the absence of regulation in the turning direction when making the 90° turn of the liquid crystal molecules. This may generate the region with different alignment such as inverse turn, that is, domain, thus disrupting the interface between the ordinary light and the extraordinary light.